Floor coverings having a wooden surface may be of several different types. Solid wood flooring is formed of a solid piece of wood in form of a plank. Engineered wood flooring is formed of a surface layer of wood glued to a core. The core may be a lamella core or a wood-based panel such as plywood, MDF or HDF. The wooden surface layer may as an example have a thickness of 2-10 mm.
A wooden floor covering may also be formed by gluing a wood veneer to a core, for example, a wood-based panel such as particleboard, MDF or HDF. Wood veneer is a thin wood layer, for example having a thickness of 0.2-1 mm. A flooring with a separate surface layer glued to a core of for example HDF or plywood is more moisture stable than solid wood floorings.
Compared to solid wood and engineered wood floorings, wood veneer floorings can be produced to a lower cost since only a thin wood layer is used. However, a wood veneer layer cannot be sanded as a solid wood or engineered wood flooring can be.
As an alternative to wood floorings, laminate floorings are also available. Direct pressed laminated flooring usually comprises a core of a 6-12 mm fibre board, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1-0.2 mm thick lower balancing layer of laminate, plastic, paper or like material.
A laminate surface conventionally comprise two paper sheets, a 0.1 mm thick printed decorative paper and a transparent 0.05-0.1 mm thick overlay intended to protect the decorative paper from abrasion. The transparent overlay, which is made of α-cellulose fibres, comprises small hard and transparent aluminium oxide particles, which gives the surface layer a high wear resistance.
The printed decorative paper and the overlay are impregnated with melamine resin and laminated to a wood fibre based core under heat and pressure. The two papers have prior to pressing a total thickness of about 0.3 mm and they are after pressing compressed to about 0.2 mm.
A wood veneer may have a lower impact resistance than laminate floorings and the production cost is high, compared to laminate floorings, when high quality veneers are to be used.
Recently new “paper free” floor types have been developed with solid surfaces comprising a substantially homogenous powder mix of fibres, binders and wear resistant particles referred to as WFF (Wood Fibre Floor). The mix is applied on a wood-based panel such as MDF or HDF, and subsequently applying heat and pressure to the mix to form a surface layer on the panel. Such a flooring and process are described in WO 2009/065769.
WO 2009/065769 also discloses a thin surface layer such as wood veneer layer, which is applied on a sub-layer comprising, for example, cork or wood fibres mixed with a binder. The sub-layer is applied on wood fibre based core.
U.S. Pat. No. 2,831,794 discloses a process for manufacturing veneer panels. A green veneer is applied on a mat of resin coated core particles of ligno-cellulose fibrous particles. Adhesive is applied on the veneer to bond the veneer to the fibrous core, and to form a dense surface zone in the fibrous core. The material of the core serves to fill knot holes or open flaws in the veneer. When heat and pressure is applied, the result is the formation of a panel, with the surface layer of the particles filling whatever flaws or holes would otherwise the present in the veneer.
U.S. Pat. No. 2,419,614 discloses a coated wood product wherein a plywood is coated by a covering or overlay material consisting of mixtures of sawdust and synthetic resin. The veneer layer is coated by the covering or overlay material such that the veneer is no longer visible. The covering forms the uppermost layer of the product.
In the above description, the different types of product have been described with reference to floorings. However, the same material and problems applies for other types of building panels such as wall panels, ceiling panels, and for furniture components.